1. Field of the Invention
This invention relates to a wax emulsion, and more particularly to a wax emulsion comprising as essential ingredients a petroleum fraction wax and a certain specified oxygen-containing wax.
2. Prior Art
Waxes separated from petroleum as heavy fractions are valuable materials used for manifold applications in crude form or after refined through various refining steps. Particularly, these waxes are used in various fields of art in the form of emulsions in which they are dispersed to be emulsified in water. These wax emulsions are generally coated on the surface of paper, fiber, wood or a variety of ceramic products or admixed to an aqueous emulsion of cement, paint or other materials. One of the important objects of the application of such an emulsion is to provide the material coated with the wax left after the water content of the emulsion with high water repellent and water-proof properties.
However, since the wax has high water repellent property of itself, the process of dispersing and emulsifying the wax is in conflict with the property of the wax. In order to obtain a stable emulsion, a large quantity amounting to more than 10% of an emulsifier must be added, and the water repellent or water-proof property of wax is considerably reduced as the quantity of the emulsifier is increased resulting in failure to attain the desired object.
In consideration of the contradiction as mentioned above, many efforts have been made to find a composition and technique for preparing an improved and stable wax emulsion by decreasing the added quantity of the emulsifier as small as possible or without adding any emulsifier in the extreme case. As the results of such efforts, many methods have been proposed including those disclosed in DT-AS No. 2,529,360 and Japanese Patent Provisonal Publication (Kokai-Koho) No. 131979/1978. The most generally employed method of emulsifying the waxes originated from the fractions of petroleum with the use of minimum quantity of an emulsifier is adding an oxygen-containing wax. The known oxygen-containing waxes used for this purpose are natural waxes, such as montan wax and bees wax, and synthetic waxes, such as oxidized paraffin and oxidized polyethylene waxes.
However, the known natural waxes have the disadvantages not only that the supply thereof is unstable but also that they have offensive odors and they contain contaminants of lower molecular weights. Moreover, the known oxygen-containing waxes have only a limited degree of freedom in varying the properties thereof, such as hardness, melting point, acid value and oil-soluble property, depending on the desired uses. Particularly, even if the properties of the known oxygen-containing waxes are varied to improve the emulsifying property and the strength of the resultant coating, satisfactory results have not been obtained. Furthermore, since the emulsifying property of the system and the properties of the resultant emulsion are changed materially by the addition of each of these known oxygen-containing waxes and by the attendant reduction in added quantity of an emulsifier, it has been required to develop a proper composition and a suitable emulsifying process. For this reason, the kind and quantity of oxygen-containing wax to be added to the emulsion has been limited.